Equal-loudness contour

The term hearing right ear right volume or loudness equalization is described as audio recordings are played back that they result in a similar listening experience at different volume levels.

The first data of the " acoustically correct volume " were brought together in 1933 by Fletcher- Munson. The " psychoacoustic curves of equal volume level" were defined in ISO Recommendation R226 ( R454 ) and DIN 45630 sheet 2 (DIN 1318 ) by Robinson - Dadson. The current data are defined in ISO 226:2003, they differ from the previous standards. The changes are caused by, inter alia, because the sensation is subjective and the data on which the standardization based is obtained by averaging over many people with different auditory impressions.

Perception of different volumes

The volume perception is strongly frequency dependent. The dependence of the loudness perception of the frequency also falls for different volume level of different.

In the picture, the frequency dependence of the sense of volume of different volumes is shown, so what sound pressure level must have pure tones of different frequencies, so they are each perceived as equally loud.

• At a volume level of 80 phon, for example, has the sound pressure level of a 50 - Hz tone will be increased by about 20 dB, so that it is equal perceived loud as a 1 kHz tone. The sound pressure level of a 10- kHz tone must be raised by about 12 dB in order to appear as loud as the 1- kHz tone.
• At a volume level of 40 phon, the sound pressure level of a 50 - Hz tone must be raised by about 33 dB, so that it is equal perceived loud as a 1 kHz tone. The sound pressure level of a 10- kHz tone must be increased by 15 dB.

Principle aurally-accurate volume equalization

Is music mixed for an original volume level of 80 phon, so that it sounds good there, the response of human hearing for this level are discussed in the recording. Will this music be played with 40 Phon volume level, do not more the settings for the 80 - phon recording. That is, to achieve a sound similar to the original recording, the bass and treble would have to be raised.

Amplifier circuits for aurally volume equalization and loudness buttons should perform an appropriate correction of the frequency response to achieve when playing at low volume levels a sound similar to the original volume.

Technical design

When playing sound through speakers or headphones, a plausible balanced listening experience should be taught. Because of the almost free choice of the playback level is caused thereby slightly an unpleasant impression when a change in coloration is caused by the change from the original level or even individual sound components vanish because of the level-dependent concealment.

To enable both vocally and in quiet adjusted amplifier has a noise corresponding to the original reproduction of all frequencies, many amplifiers are equipped with different circuits to accomplish a loudness equalization. In this case, the frequency response of the presented noise to be adapted to the playback level. Loudness by pressing a key labeled contour or this function is switched on. However, this function provides only a limited impact, since the adaptation is mostly designed to simply and applicability of the curves of equal volume level ( Isophone ) on complex signals is at least controversial. In addition, an adaptation to the Noise and the listening position is missing.

The assumption that the ups and downs must be raised equally, is not correct. The isophones run at frequencies higher than 1 kHz as well as all parallel, so at low volume playback, only the low frequency response would be to raise.